1. Field of the Invention
This invention relates to a powder coating composition. More particularly, the invention relates to a powder in-mold coating composition comprising an ethylenically unsaturated compound having a particular structure and a polymerization catalyst or said ethylenically unsaturated compound, an epoxy (meth)acrylate and a polymerization catalyst.
2. Description of the Prior Art
As described in, for example, Japanese Patent Publication No. 13928/1973, Japanese Patent Application Kokai (Laid-Open) No. 157616/1980, Japanese Patent Application Kokai (Laid-open) No. 91157/1984, etc., there have hitherto been known thermosetting in-mold coating compositions comprising (1) a base preparation obtained by uniform mixing of (a) a main component which is a blend of an unsaturated polyester resin and a liquid or solid vinyl or allyl compound as a crosslinking agent and (b) a polymerization catalyst and, if necessary, (2) additives such as a pigment, a releasing agent, a filler, a curing accelerator and the like.
When these compositions are applied on the surfaces of molded articles of polyester resin, the resulting coating layers are insufficient in surface hardness and are not sufficiently satisfactory in scratch resistance and wear resistance.
Molded articles of fiber-reinforced plastics having a gelcoat layer are generally produced by firstly spraying into a molding die of room temperature or heated to about 60.degree. C. with a liquid gelcoat resin such as an unsaturated polyester resin, a polyester acrylate resin, an epoxy acrylate resin or the like with a gun or coating said surface with said gelcoat resin with a brush to form a gelcoat layer and then applying a hand lay-up method, a spray-up method or a casting method. Since this production process is poor in productivity, a molding process was studied in which a liquid gelcoat resin is sprayed or coated onto a heated molding die, then a SMC (sheet molding compound), a BMC (bulk molding compound) or other molding compound is placed on the gelcoat layer or the die, and is molded under pressure. However, in this molding process, since the gelcoat resin contains polymerizable unsaturated monomers having a volatility such as styrene and the like, working environments are very bad and further, since the monomers vaporize, there can not be formed a gelcoat layer having a desired performance.
To improve these drawbacks, a process was developed which uses diallyl phthalate or a prepolymer thereof both having a very low volatility as the polymerizable unsaturated monomer for the gelcoat resin (Japanese Patent Publication No. 29745/1976). In this process, working environments are improved; however, the gelcoat layer formed tends to yellow when heated, is brittle and has a low hardness.